1. Field of the Invention
The present invention relates to a substrate processing unit.
2. Description of the Related Art
In a photolithography process in semiconductor device fabrication processes, for example, resist coating treatment for coating the surface of a wafer with a resist solution to form a resist film on the wafer, exposure processing for exposing the wafer in a pattern, developing treatment for developing the exposed wafer, and the like are performed to form a predetermined circuit pattern on the wafer.
At present, in the aforementioned resist coating treatment, a spin coating method in which the resist solution is discharged to the center of the wafer which is being rotated and spread over the surface of the wafer is in the mainstream.
In the spin coating method, however, since the wafer is rotated at high speed, a large quantity of resist solution is scattered from an outer edge portion of the wafer, and hence a lot of resist solution is wasted. Moreover, a unit used in this method is contaminated by the scattering of the resist solution, which causes a disadvantage that the unit needs to be cleaned frequently, or the like.
Therefore, in place of the spin coating method in which the wafer is rotated, a so-called one-stroke sketch coating method, in which the resist solution is discharge onto the wafer while the wafer and a resist solution discharge nozzle move relative to each other so that the track of a resist solution discharger has a large rectangular wave shape with large amplitude, and as a result, the resist solution is applied all over the wafer in the form of parallel lines, is thought out. In the case of this one-stroke sketch coating method, there is a possibility that the surface of a resist film after coating swells along a path of application of the resist solution, and therefore it is thought that the use of a resist solution with a low viscosity which spreads easily over the wafer after application is preferable.
However, even if the resist coating is performed by the use of the resist solution with the low viscosity, it is still expected that the surface of the resist solution swells along the path of application of the resist solution, and hence processing to planarize the resist film is required after coating. Therefore, it can be proposed that the wafer coated with the resist solution is housed in a chamber, a pressure in the chamber is reduced while an atmosphere therein is exhausted, and that by an atmospheric current formed on this occasion, the resist film is planarized.
To planarize a resist film by an atmospheric current as in such a proposal, it is desirable to attach a current plate so that the atmospheric current flows along the surface of the resist film. In this case, if a uniform atmospheric current is not formed over the entire surface of the wafer, the resist film is not planarized uniformly within the surface of the wafer, and hence the thickness of the resist film becomes nonuniform. Accordingly, it is important to form the uniform atmospheric current on the wafer within the surface of the wafer when the current plate is used.
The present invention is made in view of the aforesaid point, and its object is to make an atmospheric current generated by a reduction in pressure uniform on the surface of a substrate such as a wafer.
In view of this object, the present invention is a processing unit for processing a substrate, comprising: a chamber for housing the substrate and forming a hermetically closeable processing room; an exhauster for exhausting an atmosphere in the processing room from an upper portion of the chamber to reduce a pressure in the processing room; and a current plate for controlling an atmospheric current formed in the processing room when the pressure is reduced. The chamber includes a mounting table for mounting the substrate thereon, an almost cylindrical lid body with its lower face open for covering the substrate on the mounting plate from above and forming the processing room integrally with the mounting table, and a supporting member for supporting the current plate in such a manner that the current plate is parallel to the mounting plate.
In the present invention, the supporting member for supporting the current plate parallel to the mounting plate is provided, whereby the current plate is maintained parallel to the substrate mounted on the mounting table. Therefore, the speed of the atmospheric current flowing between the current plate and the substrate becomes uniform within the surface of the substrate, and hence, for example, a coating film applied, for example, in a manner of the aforementioned so-called one-stroke sketch is planarized uniformly within the surface of the substrate. Consequently, the coating film having a uniform film thickness can be formed on the substrate.